/*
 * Copyright (c) 2003-2013, KNOPFLERFISH project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials
 *   provided with the distribution.
 *
 * - Neither the name of the KNOPFLERFISH project nor the names of its
 *   contributors may be used to endorse or promote products derived
 *   from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.knopflerfish.bundle.cm;

import java.util.Vector;

import org.osgi.service.cm.ConfigurationException;

/**
 * This class is responsible for dispatching configurations to
 * ManagedService(Factories).
 * 
 * It is also responsible for calling <code>ConfigurationPlugins</code>.
 * 
 * @author Per Gustafson
 * @version 1.0
 */

final class UpdateQueue
  implements Runnable
{
  /**
   * The PluginManager to use.
   */
  private PluginManager pm;

  /**
   * The thread running this object.
   */
  private Thread thread;

  private final Object threadLock = new Object();

  /**
   * The queue of updates.
   */
  private Vector<Update> queue = new Vector<Update>();

  UpdateQueue(PluginManager pm)
  {
    this.pm = pm;
  }

  public void run()
  {
    while (true) {
      Update update = dequeue();
      if (update == null) {
        return;
      }
      try {
        update.doUpdate(pm);
      } catch (ConfigurationException ce) {
        Activator.log
            .error("[CM] Error in configuration for " + update.pid, ce);
      } catch (Throwable t) {
        Activator.log.error("[CM] Error while updating " + update.pid, t);
      }
    }
  }

  /**
   * Add an entry to the end of the queue.
   * 
   * @param update
   *          The Update to add to the queue.
   * @throws java.lang.Exception
   *           If given a null argument.
   */
  public synchronized void enqueue(Update update)
  {
    if (update == null) {
      return;
    }
    queue.addElement(update);
    attachNewThreadIfNeccesary();
    notifyAll();
  }

  /**
   * Get and remove the next entry from the queue. If the queue is empty this
   * method waits until an entry is available.
   * 
   * @return The Update entry removed from the queue.
   */
  private synchronized Update dequeue()
  {
    if (queue.isEmpty()) {
      try {
        wait(5000);
      } catch (InterruptedException ignored) {
      }
    }
    if (queue.isEmpty()) {
      detachCurrentThread();
      return null;
    }
    Update u = queue.elementAt(0);
    queue.removeElementAt(0);
    return u;
  }

  void attachNewThreadIfNeccesary()
  {
    synchronized (threadLock) {
      if (thread == null) {
        thread = new Thread(this);
        thread.setDaemon(true);
        thread.start();
      }
    }
  }

  void detachCurrentThread()
  {
    synchronized (threadLock) {
      thread = null;
    }
  }
}
